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      Digit ratio (2D:4D) in relation to substance and computer use: a meta-analysis

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          Abstract

          Human studies have reported inconsistent associations between the length ratio of the second finger to the fourth finger (2D:4D), which is a proxy for prenatal androgen load, and substance or computer use in adolescents and adults. This meta-analysis quantifies the magnitude of this relationship and investigates the roles of sex, definition of caseness, different forms of addiction, the hand measured (right hand versus left hand), and other cohort characteristics. Univariate random-effects meta-analyses were performed, and moderators were tested with Bonferroni-corrected meta-regression analyses. The study included 18 independent samples with a total of 175,955 participants (96,316 males and 79,639 females). There was a significant difference in 2D:4D between the substance and computer-using subjects and the controls for the combined sample (Hedge’s g = − 0.178 [− 0.291; − 0.064]) and for males (Hedge’s g = − 0.260 [− 0.399; − 0.122]), but not for females. These effects were amplified when only analyzing studies that compared dependent versus non-dependent subjects (combined sample: g = − 0.325 [− 0.492; − 0.157]; males: g = − 0.427 [− 0.564; − 0.291]), but did not reach significance in the subgroup of studies examining other parameters of substance and computer use. When analyzing different forms of substance and computer use separately, alcohol intake and computer use revealed a significant difference in the standardized mean. Again, the effects were amplified when analyzing the subgroup of males and the subgroup of studies comparing dependent versus non-dependent subjects, with effect sizes showing Hedge’s g values as many as − 0.552 [− 0.785; − 0.319] (alcohol-dependent males). Thus, this meta-analysis confirms that lower 2D:4D is associated with substance and computer dependency. Further studies are encouraged to explore the link between intrauterine hormone environment and addiction risk.

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          The online version of this article (10.1007/s00702-019-02002-2) contains supplementary material, which is available to authorized users.

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          Meta-analysis of digit ratio 2D:4D shows greater sex difference in the right hand.

          Our aims are, first, to describe the sex difference in the length ratio of the second and fourth digits (2D:4D), which likely reflects prenatal testosterone levels in humans. Second, to infer the loss of reliability observed in 2D:4D based on self-measured finger lengths. We used random-effects meta-analysis of 2D:4D based on expert-measured finger lengths (116 samples with 13,260 females and 11,789 males). We find a moderate sex difference (with lower 2D:4D for males), which shows substantial heterogeneity (which is unrelated to age). The sex difference is moderated by the type of finger length measurement and by hand. Measurement involving the distortion of soft tissue leads to a significantly larger sex difference than finger length measurement avoiding this. The sex difference in 2D:4D is larger in the right hand than in the left. The reliability of self-measured 2D:4D in the BBC internet study, by far the largest study on 2D:4D, is estimated to be 46% of that of expert-measured 2D:4D. Right-hand 2D:4D might be a better indicator of prenatal androgenisation than left-hand 2D:4D. The view that 2D:4D has allometric properties (Kratochvil L, Flegr J. 2009. Differences in 2nd to 4th digit length ratio in humans reflect shifts along the common allometric line. Biol Lett 5:643-646.) is not supported. Bone lengths contribute to the sex difference in 2D:4D. In addition, there might be a sex difference in fingers' soft tissue, which should be investigated. Because of measurement unreliability, correlations between 2D:4D and variables of interest are about one-third smaller in the BBC internet study than in studies in which 2D:4D is based on expert-measured finger lengths. (c) 2010 Wiley-Liss, Inc.
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              Fingers as a marker of prenatal androgen exposure.

              Interest in biological substrates of sex-related variations in psychological and physiological characteristics has led to a search for biomarkers of prenatal hormone exposure that can be measured postnatally. There has been particular interest in digit ratio, the relative lengths of the second and fourth fingers (2D:4D), but its validity as a measure of prenatal androgen has not been established. We report the strongest evaluation of the value of 2D:4D as a biomarker for early androgen exposure. Individuals with 46,XY karyotype but no effective prenatal androgen exposure due to complete androgen insensitivity syndrome had digit ratios that were feminized: they were higher than those of typical men and similar to those of typical women. Nevertheless, the effect was modest in size, and there was considerable within-group variability and between-group overlap, indicating that digit ratio is not a good marker of individual differences in prenatal androgen exposure.
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                Author and article information

                Contributors
                +49 9131 85-34160 , johannes.kornhuber@uk-erlangen.de
                Journal
                J Neural Transm (Vienna)
                J Neural Transm (Vienna)
                Journal of Neural Transmission
                Springer Vienna (Vienna )
                0300-9564
                1435-1463
                27 April 2019
                27 April 2019
                2019
                : 126
                : 5
                : 623-636
                Affiliations
                ISNI 0000 0001 2107 3311, GRID grid.5330.5, Department of Psychiatry and Psychotherapy, , Friedrich-Alexander University Erlangen-Nürnberg (FAU), ; Schwabachanlage 6, 91054 Erlangen, Germany
                Author information
                http://orcid.org/0000-0001-6086-0924
                http://orcid.org/0000-0002-8096-3987
                Article
                2002
                10.1007/s00702-019-02002-2
                6499759
                31028478
                4f7debfb-1ba5-473a-9d61-14786b021cae
                © The Author(s) 2019

                Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

                History
                : 4 October 2018
                : 27 March 2019
                Funding
                Funded by: FundRef http://dx.doi.org/10.13039/501100002347, Bundesministerium für Bildung und Forschung;
                Award ID: 01GL1745C
                Award Recipient :
                Funded by: FundRef http://dx.doi.org/10.13039/501100005295, Staedtler Stiftung;
                Award ID: WW/eh 29/17
                Award Recipient :
                Categories
                Psychiatry and Preclinical Psychiatric Studies - Original Article
                Custom metadata
                © Springer-Verlag GmbH Austria, part of Springer Nature 2019

                prenatal androgen exposure,2d:4d,testosterone,androgens,brain organization,substance use,alcohol,tobacco

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